JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Compounds Containing Nitrogen

A lower $\mathrm{p}{\mathrm{K}}_{\mathrm{b}}$ means a stronger base, so increasing $\mathrm{p}{\mathrm{K}}_{\mathrm{b}}$ is the order of decreasing basicity. The dialkylamine $(\mathrm{C}{\mathrm{H}}_3{)}_2\mathrm{NH}$, with two electron-donating alkyl groups on nitrogen, is the strongest base here and sits lowest; the amidine-type base (a) comes next; and (b) is the weakest of the three. The increasing order of $\mathrm{p}{\mathrm{K}}_{\mathrm{b}}$ is therefore c $<$ a $<$ b.